When an electromagnetic load is switched on, the load current does not increase suddenly; rather, it rises relatively slowly. As a result, the load comes up to its rating only with a certain time delay after the turn-on time. This peculiarity is a drawback in many technical devices.
In the case of electromagnetic injection valves of an internal-combustion engine of a vehicle, this turn-on time delay is responsible for the fact that the fuel injection time cannot be determined with sufficient accuracy. To overcome this drawback, it is known to generate the control pulse for the solenoid valve in such a way that a relatively high current surge (pull-in current) is present which leads to very rapid actuation of the solenoid valve, and which is followed by a lower, steady-state current value (hold current) for maintaining the solenoid valve in its operated position. Electronic circuits of great complexity are required for the generation of such control pulses. (German published patent application 28 28 678.)